\[\boxed{\text{1070.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\textbf{а)}\ f(x) = - 5:\]
\[0,5x - 4 = - 5\]
\[0,5x = - 1\]
\[x = - 2.\]
\[\textbf{б)}\ f(x) = 0:\]
\[0,5x - 4 = 0\]
\[0,5x = 4\]
\[x = 8.\]
\[\textbf{в)}\ f(x) = 2,5:\]
\[0,5x - 4 = 2,5\]
\[0,5x = 6,5\]
\[x = 13.\ \]